Vitreous grinding composition



United States Patent VITREOUS GRINDING COMPOSITION George August Rieke, Chicago, Ill.

No Drawing. Application May 17, 1951, Serial No. 226,949

6 Claims. (Cl. 51-308) This invention relates to vitreous compositions which may be used for grinding tools, such as grinding wheels, and it relates more particularly to such wheels or tools fabricated of inorganic abrasive in finely divided form mixed with an inorganic bonding material and vitrified at elevated temperature into a composite structure.

According to present practice, wheels or tools of the type described are fabricated by mixing inorganic abrasive particles and inorganic binding material in suitable proportions, molding the mixture to the desired shape for the final product, drying the mold form at room conditions and then at elevated temperatures, and finally firing the mass in a kiln to produce a substantially porous and rigid product having high strength and characterized by an abrading or cutting action. During the firing operation, the inorganic bonding maerial, usually in the form of clays or the like, are partially reduced to molten condition which freezes upon cooling into a hard bonding substance which secures the abrasive particles in set relation and also imparts some of the characteristics of an abrasive itself. At the temperature of firing, substantially all foreign material and inorganic substances which might have been included in the original formulation are substantially completely eliminated so that the final product is composed almost entirely of the fired abrasives and bonding material in combination.

Although wheels and tools of the type described are widely used in the industry for abrasion and cutting of inorganic or metallic substances, there are a number of properties lacking in such products which it is desired to improve. For example, it is desirable to increase the Wearing qualities of the wheel so as to increase its useful life While, at the same time, increasing the speed of operation of the Wheel for cutting thereby to increase the rate of cutting as well as the life of the wheel. The development of such properties coupled with the ability of the wheel to maintain a good cutting edge makes for more efiicient use of time and materials in the processing industry.

It is an object of this invention to produce an improved vitrified grinding wheel or tool of the type described composed substantially of inorganic materials and it is a related object to produce a vitrified grinding wheel which is characterized by improved wear, better cutting action and ability of use at higher cutting speeds than has heretofore been available with wheels of similar type.

It has been found that the manufacture of a vitrified grinding wheel embodying the desirable characteristics described may be formulated of a composition containing as an essential ingredient an exfoliated micaceous mineral in finely divided form and uniformly distributed with the inorganic abrasive and inorganic bonding material prior to molding and firing in the formation of a final product.

In a vitrified composition of the type produced by this invention, the amount of inorganic binding material may vary within the range of -50 percent by weight of the final product with the inorganic abrasive making up the remainder other than the amount of micaceous mineral incorporated therewith. For hard wheels, the ratio of bonding material to abrasive is in the upper portion of the defined range, such for example when present in amounts of 40-50 parts by weight bonding material to 60-50 parts by weight abrasive. On the other hand, in the manufacture of a soft wheel, the bonding material may lie in the range of 5-20 parts by weight to -80 parts by weight abrasive.

The amount of exfoliated micaceous mineral which has been found beneficially to affect the properties of the final product varies in accordance with the concentration of the bonding material. It is preferred to incorporate from 10-15 percent by weight of the exfoliated micaceous mineral based upon the weight of the bonding material for some uses but suitable products may be secured when the exfoliated micaceous mineral is present in the ratio of 5-25 percent by weight of the bonding material.

The exfoliated micaceous ingredient may be selected from a number of micaceous minerals, such as vermiculite, culsageeite, jetfersite, kervite, wilcoxite, and the like, but it is preferred to make use of exfoliated vermiculite such as believed to be formed by alteration of biotite and phlogopite as is usually found in association with basic rock, such as dunite, serpentine and the like. Methods for exfoliation of micaceous minerals for use in the manufacture of vitrified grinding wheels forms no part in this invention and detailed description thereof is believed to be unnecessary. Suflice it to say that such processes are well known, one method being fully described in Patent No. 1,922,448 granted August 15, 1933, and Patent No. 1,963,276, granted June 19, 1934, to Carl S. Miner.

By way of illustration but not by way of limitation, the following is an analysis of an exfoliated micaceous product which may be used in the practice of this invention.

The effect of the exfoliated micaceous mineral forming a part of the vitrified wheel is not fuliy understood. It is known that when present in the defined proportions and infinely divided form and fired with the abrasive and binder, a vitrified inorganic grinding wheel or tool is produced which can be operated at cutting speeds considerably greater than that for wheels of similar composition without the exfoliated micaceous mineral; the wear of the improved Wheel is less when compared to the standard wheel with the resui't that greater cutting speeds can be obtained without reducing the useful life thereof.

it has been found that equivalent results are not available from the use of micaceous minerals which have not been exfoliated. There is reason to believe that the presence of exfoliated mica in finely divided form in the final product plasticizes or otherwise modifies the interbonded relation of the inorganic substances in a manner to in- 3 crease the strength and the hardness of the final product. For this purpose, it is believed desirable to maintain the minute particle size of the micaceous mineral and to eliminate hard components therefrom, such as aluminum oxide and the like which are substantially eliminated by the exfoliating step. Mica which has not been exfoliated has a melting point in the range 1800 F. as compared to the melting point of 2600-3500 F. or more for its exfoliated derivative. It is believed that unexfoliated mica, especially when incorporated in finely divided form, so reacts or becomes changed during the firing of the wheel that its identity is substantially lost and no improvement is secured by its use. On the other hand, microscopic examination of tools produced by this invention indicate that the exfoliated micaceous ingredients remain substan-. tially in the finely divided form in which they are incorporatcd. It may be possible that some reaction alone or in combination with the abrasive or heading material takes place during vitrification and lends itself towards the new result.

The following examples illustrate compositions which may be used in the practice of this invention:

Example 1 percent exfoliated mica in finely divided form percent bentonite 75 percent silicon carbide Example 2 8 percent exfoliated mica 40 percent China clay 52 percentCarborundum Example 3 6 percent exfoliated vermiculite 60 percent clay 34 percent silicon carbide Example 4 2 percent exfoliated mica 20 percent clay 78 percent Carborundum ing agent and pressure molded into a wheel or the like.

The molded product is allowed to air dry for a day or more and is then heated to a temperature ranging from 250-750" F. for drying. The dried and molded product is fired at usual temperatures of the industry for vitrification.

It will be understood that other inorganic binders of the clay type may be used and that other inorganic abrasive particles, such as diamonds, zircon and the like might also be substituted without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. A vitrified grinding tool formed of a composition consisting essentially of finely divided inorganic abrasive particles selected from the group consisting of silicon carbide, Carborundum, diamonds and zircon, an inorganic clay binder and an exfoliated micaceous mineral in which the materials are present in the ratio of 5-50 parts by weight of the inorganic clay binder, -50 parts by weight of the inorganic abrasive and 5 25 parts by weight of exfoliated micaceous mineral .to parts by weight of the clay binder and which hasbeen heated in admixture to a temperature for vitrification.

2. A vitrified grinding tool formed of a composition consisting essentially of finely divided inorganic abrasive particles selected from the group consisting of silicon carbide, Carborundum, diamonds and zircon, an inorganic clay binder and an exfoliated micaceous mineral in which the materials are present in the ratio of 5-50 parts by weight of the inorganic clay binder, 95-50 parts by weight of the inorganic abrasive and 5-25 parts by weight of exfoliated micaceous mineral to 100 parts by Weight of the clay binder, which has been heated in admixture to a temperature for vitrification and in which the particles of exfoliated micaceous mineral remain identifiable in the vitrified product as distinguished from the loss of identity of mica when incorporated without previous exfoliation.

3. In the method of fabricating an abrasive grinding tool comprising mixing a small amount of water with solids in particle form consisting essentially of finely divided inorganic abrasive particles selected from the group consisting of silicon carbide, Carborundum, diamonds and zircon, an inorganic. clay binder and an exfoliated micaceous mineral in which the materials are present in the ratio of 5-50 parts by weight of the inorganic clay binder to 95-50 parts by weight of the inorganic abrasive, and 5-25 parts by weight of exfoliated mica to 100 parts by weight of the clay binder, molding the mixture to a desired shape for the final. product, drying themolded product, then heating the dried product to a temperature sufficient for vitrification, and then cooling the vitrified product.

4. The method as claimed in claim 3 which includes the step of heating the molded product to a temperature of 250-750 F. for drying prior to vitrification.

5. A vitrified composition as claimed in claim 1 in which the abrasive comprises Carborundum.

6. A vitrified composition .of matter as claimed in claim 1 in which the exfoliated micaceous mineral comprises exfoliated vermiculite having a particle size distribution of Percent Larger than .05 mm 0 .05-.005 38 .001-smaller 13 References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Graphitic mica--a reinforcing pigment for protective coating, W. Dell et al., Paint and Oil and Chemical Review, Oct. 19, 1944, pp. 12-18. 

2. A VITRIFIED GRINDING TOOL FORMED OF A COMPOSITION CONSISTING ESSENTIALLY OF FINELY DIVIDED INORGANIC ABRASIVE PARTICLES SELECTED FROM THE GROUP CONSISTING OF SILICON CARBIDE, CARBORUNDUM, DIAMONDS AND ZIRCON, AN INORGANIC CLAY BINDER AND AN EXFOLIATED MICACEOUS MINERAL IN WHICH THE MATERIALS ARE PRESENT IN THE RATIO OF 5-50 PARTS BY WEIGHT OF THE INORGANIC CLAY BINDER, 95-50 PARTS BY WEIGHT OF THE INORGANIC ABRASIVE AND 5-25 PARTS BY WEIGHT OF EXFOLIATED MICACEOUS MINERAL TO 100 PARTS BY WEIGHT OF THE CLAY BINDER, WHICH HAS BEEN HEATED IN ADMIXTURE TO A TEMPERATURE FOR VITRIFICATION AND IN WHICH THE PARTICLES OF EXFOLIATED MICACEOUS MINERAL REMAIN IDENTIFIABLE IN THE VITRIFIED PRODUCT AS DISTINGUISHED FROM THE LOSS OF IDENTITY OF MICA WHEN INCORPORATED WITHOUT PREVIOUS EXFOLIATION. 